Illumination system using phosphor remote form light source

ABSTRACT

The invention provides an illumination system and a method for illumination. The illumination system includes one or more light sources that produce a primary light, a light-mixing zone that homogenizes the primary light, a wavelength-converting layer that converts the primary light to a secondary light, and a light-transmitting zone that receives the secondary light and transmits the secondary light to, for example, a Liquid Crystal Display (LCD).

BACKGROUND

The invention relates generally to the field of illumination systems,and more specifically, to illumination systems using awavelength-converting material, such as phosphor, located remotely fromthe light source, such as a light emitting diode.

Illumination systems are widely used to backlight display devices suchas televisions, laptops, and Personal Digital Assistants (PDAs); tolight up shelves in cabinets and kitchens; and for signage and contourlighting. An illumination system may include a light source that iscoupled to an optical waveguide. The optical waveguide transmits thelight produced by the light source to, for example, a display device.

Some existing illumination systems include Cold Cathode FluorescentLamps (CCFLs) as light sources. The light emitted by CCFLs is coupledinto an optical waveguide, which transmits the light. However, CCFLscontain mercury, which may cause environmental hazards. Moreover, CCFLsare large in size and require high operational voltages.

Illumination systems that include Light Emitting Diodes (LEDs) as lightsources are gaining in popularity. An example of the existingillumination systems that include LEDs as light sources are illuminationsystems that have a plurality of LEDs producing, for example, a whitelight or red, blue and green lights. The red, blue and green lights maybe mixed to generate, for example, a substantially white light. Further,the existing illumination systems include packaging around the lightsources to improve the efficiency of the existing illumination systems.

The packaging around the light sources increases the size of theexisting illumination systems. In the existing illumination systemsusing LEDs, the red, blue and green lights have to be uniformly mixed togenerate a substantially white light. However, it is difficult toachieve consistency in the spatial spectral distribution and brightnessof the light in the existing illumination systems. Moreover, due totransmission losses, the efficiency of the existing illumination systemsis low.

SUMMARY

An object of the invention is to provide an illumination system.

Another object of the invention is to provide an illumination system,which produces a uniform bright light with a consistent spatial spectraldistribution, while using a considerably less amount of space than theexisting illumination systems.

Various embodiments of the invention provide an illumination system anda method for illumination. In accordance with an embodiment of theinvention, the illumination system includes one or more light sources, alight-mixing zone, a wavelength-converting layer, and alight-transmitting zone. The light sources produce a primary light. Thewavelength-converting layer converts the primary light to a secondarylight. The light-transmitting zone substantially transmits the secondarylight towards, for example, a Liquid Crystal Display (LCD). Further, oneor more intermediate layers may be included between thelight-transmitting zone and the LCD, for example, to distribute thesecondary light uniformly over the LCD.

In accordance with another embodiment of the invention, the method forillumination includes producing and homogenizing a primary light,converting the primary light to a secondary light, and substantiallytransmitting the secondary light towards, for example, an LCD.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the invention will hereinafter be described inconjunction with the appended drawings, provided to illustrate and notto limit the invention, wherein like designations denote like elements,and in which:

FIG. 1 a illustrates an illumination system, in accordance with anembodiment of the invention;

FIG. 1 b illustrates a display system, in accordance with FIG. 1 a;

FIG. 2 a is a cross section of an illumination system, in accordancewith FIG. 1 a;

FIG. 2 b is a cross section of an illumination system, in accordancewith an alternative embodiment of the invention;

FIG. 3 a is a cross section of an illumination system, in accordancewith FIG. 1 a and FIG. 1 b;

FIG. 3 b is a cross section of an illumination system, in accordancewith another alternative embodiment of the invention;

FIG. 3 c is a cross section of an illumination system, in accordancewith FIG. 3 a;

FIG. 3 d is a cross section of an illumination system, in accordancewith FIG. 3 a; and

FIG. 4 is a flowchart of a method for illumination, in accordance withan embodiment of the invention.

DESCRIPTION OF VARIOUS EMBODIMENTS

Various embodiments of the invention provide an illumination system anda method for illumination. In accordance with an embodiment of theinvention, the illumination system may be used, for example, toilluminate a Liquid Crystal Display (LCD).

FIG. 1 a illustrates an illumination system 100, in accordance with anembodiment of the invention. Illumination system 100 includes one ormore light sources 102, hereinafter referred to as light sources 102, alight-mixing zone 104, a wavelength-converting layer 106, and alight-transmitting zone 108. Light-transmitting zone 108 includes afirst surface 110, one or more transmitting surfaces such as atransmitting surface 112, and one or more remaining edge surfaces suchas a remaining edge surface 114. In accordance with various embodimentsof the invention, first surface 110, the one or more transmittingsurfaces and the one or more remaining edge surfaces combine to form aclosed structure.

Light sources 102 produce a primary light, which may be, for example, ablue light, an Ultra Violet (UV) light or a near-UV light. Light-mixingzone 104 is coupled to light sources 102, and receives the primary lightfrom light sources 102. The primary light is homogenized in light-mixingzone 104, for example, to achieve a spatially uniform spectraldistribution and a uniform brightness of the primary light. Light-mixingzone 104 distributes the homogenized primary light uniformly overwavelength-converting layer 106, which is coupled to light-mixing zone104. The homogenization of the primary light in light-mixing zone 104 isexplained in detail in conjunction with FIG. 2 a.

Wavelength-converting layer 106 converts the primary light to asecondary light. The secondary light may be, for example, a white light.In accordance with an embodiment of the invention, wavelength-convertinglayer 106 may be a phosphor layer such as a red and green phosphorlayer, a blue, red, and green phosphor layer and an Yttrium AluminiumGarnet (YAG) phosphor layer. Wavelength-converting layer 106 may beplanar or may have a different shape.

First surface 110 of light-transmitting zone 108 is associated withwavelength-converting layer 106. Herein, the association may include,for example, the introduction of zero or more intermediate layersbetween wavelength-converting layer 106 and first surface 110. Firstsurface 110 receives the secondary light from wavelength-convertinglayer 106. Transmitting surface 112 transmits the secondary lightreceived by first surface 110 such that the secondary light may be used,for example, to illuminate an LCD. In accordance with an embodiment ofthe invention, transmitting surface 112 may be situated adjacent tofirst surface 110. In particular, the central plane of transmittingsurface 112 may be substantially perpendicular to the central plane offirst surface 110.

In accordance with an embodiment of the invention, each of light sources102 may include one or more Light Emitting Diodes (LEDs). Further, eachof the LEDs may be a blue LED, an Ultra Violet (UV) LED, a near-UV LED,and the like. In accordance with an embodiment of the invention, theLEDs included in light sources 102, may be coated with an encapsulatingmaterial. The encapsulating material may perform the functions of, forexample, extracting light from the LEDs, and optimizing the radiationprofile to get higher coupling efficiency, or better uniformity.Further, the encapsulating material may include, for example, aphosphor, to produce the primary light with the desired spatial spectraldistribution.

In accordance with another embodiment of the invention, light sources102 may include LED power packages. Examples of the LED power packagesinclude Luxeon™-type LEDs, and the like. Herein, the luminous flux ofthe LED power packages is substantially higher than that of conventionalLEDs.

In accordance with an embodiment of the invention, the amount of theprimary light produced by an LED, as one of light sources 102, may beregulated in response to the illumination required from illuminationsystem 100. The regulation of the amount of the primary light producedby the LED may be achieved by, for example, varying the current throughthe LED. Further, the amount of the primary light produced by lightsources 102 may be regulated by varying the number of LEDs included ineach of light sources 102.

In accordance with an embodiment of the invention, light-mixing zone 104may be, for example, a light guide, a hollow light guide, a hollowplastic casing, and the like. Light-mixing zone 104 may be made of, forexample, a synthetic resin, acryl, polycarbonate, PMMA, glass, and thelike. Further, light-mixing zone 104 may be a solid zone or may includean air cavity. In accordance with an embodiment of the invention, thethickness of light-mixing zone 104, hereinafter referred to as t, maylie between 1 mm to 10 mm. In accordance with an embodiment of theinvention, t is equal to 2.5 mm. Herein, t is the dimension along they-axis (as shown in FIG. 1 a)

In accordance with an embodiment of the invention, wavelength-convertinglayer 106 includes a base material and a fluorescent material. Thefluorescent material is distributed in the base material, for example,in the form of particles. The fluorescent material converts the primarylight, such as a blue light, to the secondary light, such as the whitelight. Examples of the base material may include optically clearsilicone, acrylic, polycarbonate, and the like. The fluorescent materialis selected according to the desired spatial spectral distribution ofthe secondary light. An example of the fluorescent material may includeYttrium Aluminum garnet (YAG) grains. Herein, the YAG grains may be, forexample, Cerium (Ce)-activated and may contain doped gadolinium. Inaccordance with various embodiments of the invention,wavelength-converting layer 106 may be deposited by using, for example,a screen-printing process or a sol-gel method. Further, theconcentration of the fluorescent material in wavelength-converting layer106 may be varied according to, for example, the desired spatialspectral distribution of the secondary light. In accordance with anembodiment of the invention, wavelength-converting layer 106 includesonly a layer of the fluorescent material.

In accordance with an alternative embodiment of the invention, differentfluorescent materials may be included in a single wavelength-convertinglayer, such as wavelength-converting layer 106.

In accordance with an embodiment of the invention, wavelength-convertinglayer 106 may further include, for example, rare earth metals to improveproperties such as color rendering of wavelength-converting layer 106.

In accordance with various embodiments of the invention, the fluorescentmaterial may convert the primary light, incident on the fluorescentmaterial, to an intermediate light. Thereafter, the intermediate lightmay be combined with an unconverted primary light to generate thesecondary light. The unconverted primary light may include, for example,the primary light that is not incident on the fluorescent material (forexample, the primary light passes through wavelength-converting layer106), and hence is not converted to the intermediate light. For example,when the blue light is incident on wavelength-converting layer 106, aportion of the blue light that is incident on the fluorescent material,such as YAG grains, may be converted to a yellow or an amber light bythe YAG grains. The yellow light may then be combined with theunconverted blue light, to generate a substantially white light. Herein,the white light may have varying shades depending on the thickness ofwavelength-converting layer 106, and the amount of the fluorescentmaterial present in wavelength-converting layer 106. In accordance withan embodiment of the invention, the fluorescent material absorbs theprimary light with a first wavelength and emits the intermediate lightwith a second wavelength, the second wavelength being longer than thefirst wavelength.

In accordance with an embodiment of the invention, when the primarylight is the UV light, the fluorescent material may include blue, redand green phosphor grains, to generate the secondary light.

In accordance with various embodiments of the invention, theintermediate light may be combined with the unconverted primary lightwithin wavelength-converting layer 106, or a separate diffuser layer maybe used to combine the intermediate light with the unconverted primarylight.

In accordance with an embodiment of the invention, light-transmittingzone 108 may include, for example, an optical waveguide, a light guide,a hollow light guide, and the like. Light-transmitting zone 108 may bemade of, for example, a synthetic resin, acryl, polycarbonate, PMMA,glass, and the like. In accordance with various embodiments of theinvention, remaining edge surface 114 may be inclined at zero or moredegrees with respect to transmitting surface 112. In particular,light-transmitting zone 108 may have a wedge-shaped geometry.

In accordance with an embodiment of the invention, the secondary lightmay go through Total Internal Reflection (TIR) in light-transmittingzone 108. Herein, TIR is a phenomenon that causes reflection of a light,such as the secondary light, when the light traveling in a first mediumwith a higher refractive index, strikes an interface with a secondmedium with a lower refractive index. A necessary condition for TIR tooccur is that the angle of incidence of the light with respect to thenormal to the interface is greater than a critical angle of thecombination of the first medium and the second medium. In accordancewith an embodiment of the invention, the secondary light is transmittedthough transmitting surface 112 by frustrating TIR. In accordance withan embodiment of the invention, wedge-shaped geometry oflight-transmitting zone 108 facilitates frustration of TIR andsubsequent transmission of the secondary light through transmittingsurface 112.

FIG. 1 b illustrates a display system 116, in accordance with FIG. 1 a.Display system 116 includes an illumination system, such as illuminationsystem 100 (shown in FIG. 1 a), one or more intermediate layers 118,hereinafter referred to as intermediate layers 118, and a display 120.Examples of display system 116 may include, but are not limited to,LCDs. Illumination system 100 is used to illuminate display 120. Thesecondary light, transmitted by illumination system 100, is made to passthrough intermediate layers 118 before being used to illuminate display120. In accordance with various embodiments of the invention,intermediate layers 118 may include one or more polarizing filters, oneor more Thin Film Transistor (TFT) arrays, one or more layers includingliquid crystals, Red Green Blue (RGB) filters, and the like. Inaccordance with various embodiments of the invention, display 120 may bea transmissive display or a transflective display.

FIG. 2 a is a cross section of illumination system 100, in accordancewith FIG. 1 a. Herein, the cross section is taken along a plane that isparallel to a plane x-y (as shown in FIG. 2 a). Illumination system 100further includes a plurality of coupling members 202, hereinafterreferred to as coupling members 202, one or more reflective surfaces204, hereinafter referred to as reflective surfaces 204, one or morereflective surfaces 206, hereinafter referred to as reflective surfaces206, and one or more diffusive layers 208, hereinafter referred to asdiffusive layers 208. Coupling members 202 are provided to uniformlycouple the secondary light out of light-transmitting zone 108. Further,coupling members 202 may be used to improve the outcoupling efficiency.Reflective surfaces 204 may be used, for example, to couple thesecondary light out of light-transmitting zone 108 in a desireddirection through, for example, transmitting surface 112. In accordancewith an embodiment of the invention, the one or more remaining edgesurfaces of light-transmitting zone 108 (as described in FIG. 1 a) mayinclude reflective surfaces 204. Examples of a reflective surface 204may include a mirrored surface, a white colored surface, and the like.Reflective surfaces 204 may also be used to homogenize the secondarylight, prior to transmission. In accordance with an embodiment of theinvention, the one or more remaining edge surfaces may be transparent,and may include one or more reflective films, which reflect thesecondary light into light-transmitting zone 108.

Light-mixing zone 104 includes reflective surfaces 206. Homogenizationand uniform distribution of the primary light over wavelength-convertinglayer 106 may be achieved in light-mixing zone 104 by reflecting theprimary light off the respective reflective surfaces 206 towardswavelength-converting layer 106. Examples of a reflective surface 206may include a mirrored surface, a white colored surface, and the like

The secondary light, coupled out of light-transmitting zone 108, is madeto pass through diffusive layers 208. In accordance with an embodimentof the invention, diffusive layers 208 may be implemented inintermediate layers 118 (as shown in FIG. 1 b). Diffusive layers 208 maybe used to uniformly distribute the secondary light over, for example,display 120.

In FIG. 2 a, arrows diagrammatically indicate the path of one or morelight rays. A primary light ray, produced by one of light sources 102,enters light-mixing zone 104. In light-mixing zone 104, the primarylight ray may be reflected, once or multiple times, and may subsequentlybe coupled into wavelength-converting layer 106, which generates asecondary light ray. The secondary light ray may be reflected orscattered once or multiple times, and may be coupled out oflight-transmitting zone 108, for example, by using coupling members 202and reflective surfaces 204.

Coupling members 202 couple the secondary light out oflight-transmitting zone 108 by using, for example, reflection,refraction and scattering. In accordance with an embodiment of theinvention, coupling members 202 may be used in conjunction withreflective surfaces 204, to couple the secondary light out oflight-transmitting zone 108. In accordance with various embodiments ofthe invention, coupling members 202 may include, for example, surfacedeformations including wedges and ridges, screen-printed dots, and thelike. Coupling members 202 may be provided by using processes such asprinting, pressing, etching, scribing, sandblasting, and the like.

In accordance with alternative embodiments of the invention, one or moresurfaces of light-mixing zone 104 may include coupling members 202, tocouple the primary light out of light-mixing zone 104 uniformly towardswavelength-converting layer 106. Further, one or more surfaces oflight-mixing zone 104 may include coupling members 202, to couple theprimary light into light-mixing zone 104, and to homogenize the primarylight in light-mixing zone 104.

In accordance with various embodiments of the invention,wavelength-converting layer 106 may include coupling members 202, tocouple the primary light into wavelength-converting layer 106. Further,wavelength-converting layer 106 may include coupling members 202 tocouple the secondary light out of wavelength-converting layer 106. Inaccordance with an embodiment of the invention, one or more surfaces ofwavelength-converting layer 106 may be made rough or may havemicrostructures, which may serve as coupling members 202.

FIG. 2 b is a cross section of illumination system 100, in accordancewith FIG. 1 a. Herein, the cross section is taken along a plane that isparallel to plane x-y. In FIG. 2 b, an alternative geometry oflight-transmitting zone 108 is illustrated, where the cross section isrectangular in shape. In accordance with an alternative embodiment ofthe invention, the cross section may have a trapezoidal geometry.

FIG. 3 a is a cross section of illumination system 100, in accordancewith FIG. 1 a and FIG. b. The cross section is taken along a plane thatis parallel to plane z-x. Herein, wavelength-converting layer 106 andlight-transmitting zone 108 are associated such that an airgap 302 isintroduced between wavelength-converting layer 106 andlight-transmitting zone 108. Airgap 302 may be used, for example, toensure that the secondary light is within the critical angle of thelight-transmitting zone 108.

FIG. 3 b is a cross section of illumination system 100, in accordancewith FIG. 1 a. The cross section is taken along a plane that is parallelto plane z-x. Herein, light sources 102 are arranged in a manner so asto form an array. In accordance with an embodiment of the invention, thecentral plane of the array is substantially parallel to the frontsurface of wavelength-converting layer 106.

In accordance with an embodiment of the invention, light-mixing zone 104may further include sensors situated, for example, between any two lightsources 102 in the array. The sensors may be used to ensure that theprimary light produced by light sources 102 has a consistent brightnesslevel and spatial spectral distribution.

FIG. 3 c is a cross section of illumination system 100, in accordancewith FIG. 3 a. One or more Brightness Enhancement Films (BEFs) 304,hereinafter referred to as BEFs 304, are introduced betweenwavelength-converting layer 106 and light-transmitting zone 108. BEF 304may be used, for example, to focus the secondary light intolight-transmitting zone 108. This increases the brightness of thesecondary light in light-transmitting zone 108, and subsequently, thebrightness of the secondary light transmitted by light-transmitting zone108.

In accordance with another embodiment of the invention,wavelength-converting layer 106 and light-transmitting zone 108 may beassociated by introducing one or more filters betweenwavelength-converting layer 106 and light-transmitting zone 108. Thefilters capture the unconverted primary light that may be coupled out ofwavelength-converting layer 106. Herein, capturing may include absorbingthe primary light or reflecting the primary light towavelength-converting layer 106.

FIG. 3 d is a cross section of illumination system 100, in accordancewith FIG. 3 a. The cross section is taken along a plane that is parallelto plane z-x. Herein, illumination system 100 includes a light guide 306a and a light guide 306 b. Each of light guide 306 a and light guide 306b have one tapered surface and are overlaid. In accordance with anembodiment of the invention, light guide 306 a and light guide 306 buniformly distribute the primary light over wavelength-converting layer106 and ensure substantial homogenization of the primary light inlight-mixing zone 104. Each of light guide 306 a and light guide 306 bmay be made of, for example, silicone, acrylic, polycarbonate, and thelike. In accordance with an embodiment of the invention, each of lightguide 306 a and light guide 306 b are coupled to one or more lightsources 102.

In accordance with an embodiment of the invention, one or more lightguides, such as light guide 306 a and light guide 306 b, may be used touniformly distribute the primary light over wavelength-converting layer106, and achieve substantial homogenization. Further, one or more lightsources 102 may be used in conjunction with the one or more lightguides. In accordance with an alternative embodiment, one or moresurfaces of each of the one or more light guides may be tapered.

FIG. 4 is a flowchart of a method for illumination, in accordance withan embodiment of the invention. At 402, a primary light is produced byusing, for example, light sources 102. At 404, the primary light ishomogenized by using, for example, light-mixing zone 104. At 406, theprimary light is converted to a secondary light by using, for example,wavelength-converting layer 106. Herein, converting the primary light tothe secondary light involves converting the primary light to anintermediate light. The intermediate light is then combined with theunconverted primary light to generate the secondary light. At 408, thesecondary light is transmitted by using, for example, light-transmittingzone 108. In particular, the secondary light may be transmitted through,for example, transmitting surface 112. The transmitted secondary lightmay be used for illumination.

Various embodiments of the invention provide an illumination system anda method for illumination. The illumination system, such as illuminationsystem 100, produces a uniform bright light with a uniform spatialspectral distribution. This is achieved by homogenizing the primarylight in light-mixing zone 104, and uniformly distributing the primarylight over wavelength-converting layer 106. The secondary light is alsohomogenized prior to transmission. Further, the illumination system issmaller in size. This is achieved by avoiding the use of packagingaround light sources 102. In addition, the illumination system has ahigh efficiency. This is achieved by reducing transmission losses, forexample, while coupling the light into light-mixing zone 104 from lightsources 102.

By providing wavelength-converting layer 106 remote from the LEDs,rather than as part of each LED, various types of LEDs may be used, andthe wavelength-converting layer 106 may be more easily constructed.Further, the remote wavelength-converting layer 106 provides additionalmixing of the primary light generated by the LEDs.

Illumination system 100 may be provided as a single interconnected orintegral unit of any size. Illumination system 100 may be used forilluminating an LCD for a cellular telephone, television, or otherdevices.

While various embodiments of the invention have been illustrated anddescribed, it will be clear that the invention is not limited only tothese embodiments. Numerous modifications, changes, variations,substitutions and equivalents will be apparent to those skilled in theart, without departing from the spirit and scope of the invention, asdescribed in the claims.

1-26. (canceled)
 27. A lighting device comprising: a first substrate; aplurality of non-packaged light emitting dies, each die having at leasta first die electrode and a second die electrode; and a secondsubstrate, wherein the plurality of dies are sandwiched between thefirst substrate and the second substrate to encapsulate the dies,wherein at least one of the first substrate and second substrategenerally conforms to a thickness of the dies without any intermediatesubstrate layer needed for a spacer, wherein electrical connectionsbetween at least some of the dies are formed by conductors supported byat least one of the first substrate and second substrate, and wherein atleast one of the first substrate and second substrate has light passinglocations for emitting light.
 28. The device of claim 27 wherein, thefirst substrate has first connection locations electrically connected tofirst conductors formed on the first substrate, wherein the first dieelectrode of associated dies are aligned with and electrically connectedto an associated first connection location on the first substratewithout wire bonds, wherein the second substrate has second connectionlocations electrically connected to second conductors formed on thesecond substrate, the second die electrode of associated dies beingaligned with and electrically connected to an associated secondconnection location on the second substrate without wire bonds, andwherein portions of the first conductors and portions of the secondconductors overlap and electrically connect when the first substrate andthe second substrate are brought together to create a series connectionof the dies without using wire bonds.
 29. The device of claim 28 whereinthe first connection locations are connected to the first die electrodesof associated dies by a conductive paste.
 30. The device of claim 28wherein the first conductors extend to first areas away from the diesand the second conductors extend to second areas away from the dies sothat, when the first substrate and the second substrate are broughttogether, the first areas and the second areas are aligned, andelectrical contact is made between the first conductors and secondconductors.
 31. The device of claim 28 wherein the dies are verticaldiodes having a cathode electrode on a first surface and an anodeelectrode on an opposite surface, wherein at least some of the firstconductors are connected to the cathode electrodes and at least some ofthe second conductors are connected to the anode electrodes, wherein thefirst conductors align with the second conductors when the dies aresandwiched between the first substrate and the second substrate toconnect an anode of a first die to a cathode of an adjacent second dieto connect the first die and the second die in series.
 32. The device ofclaim 27 wherein at least one of the first substrate and secondsubstrate is formed of a deformable material that deforms whenconforming to the thickness of the dies.
 33. The device of claim 27further comprising an adhesive layer between the first substrate and thesecond substrate.
 34. The device of claim 27 wherein the thickness ofthe dies is equal to or less than 200 microns.
 35. The device of claim27 wherein the second substrate has lenses formed in it.
 36. The deviceof claim 27 wherein the second substrate has a flat light emittingsurface.
 37. The device of claim 27 wherein the first substrate and thesecond substrate are flexible.
 38. The device of claim 27 wherein atleast one of the first substrate and second substrate is less than 2 mmthick.
 39. The device of claim 27 further comprising an encapsulant thatfills any voids around the dies to encapsulate the dies.
 40. The deviceof claim 27 further comprising a phosphor over a surface of the secondsubstrate for creating white light.
 41. The device of claim 27 whereinthe first substrate comprises at least one reflector for reflectinglight through the second substrate.
 42. The device of claim 27 wherein afirst edge of the first substrate and a second edge of the secondsubstrate are connected together so that the first substrate and thesecond substrate are aligned when they are brought together forsandwiching the dies between the first substrate and the secondsubstrate.
 43. The device of claim 27 further comprising an electricalconnection causing a plurality of strings of series-connected dies to beconnected in parallel.